There presently exists many varieties of paper clips commercially available and in use today. By far the most highly successful clip has been the conventional bent wire paper clip, which has dominated the field for many years. Variations of the wire paper clips have from time to time been introduced, however, never gaining wide acceptance in the market. However, recently a new paper clip has been introduced that is essentially a thin plate of spring steel bent into a U-shaped cross section that has gained some market share in Japan and is now on sale in the United States. In operation, the plate portions of this paper clip are separated apart and then the clip is slid over for example a document. The edges of the clip are inserted tapered slightly outwardly to form ramp portions to facilitate sliding the edges of the paper therebetween when applying the clip.
Another popular clip designed for handling thick documents is similar to the above-described new paper clip, except the edge portions of the plates forming the clip are provided with bent wire actuators. The bent wire actuators can be pivoted from one position, during use of the clip, to a clip removal position where the bent wire portions use the body of the clip itself as fulcrums for separating the plate edges by pressing the free ends of the bent wire actuators together for removing the clip. These clips are constructed of all metal, and require a number of separate components and bending manufacturing steps of the spring steel plate and the bent wire actuators increasing the costs of manufacturing.
The paper clip according to the present invention can accommodate various width plural sheet documents ranging from a couple of sheets to tens of sheets and provide adequate biasing force in any range of normal document thickness. In contrast, the conventional wire paper clip can only accommodate documents having up to approximately twenty (20) sheets due to the limitation on the amount of bending the inner wire loop can sustain at its base prior to permanent plastic deformation of the wire section located at the base. In order to accommodate thicker documents, the conventional wire paper clip must be somewhat reformed by the fingers of the user, resulting in a clip with inadequate biasing force. The deficiency of the use of the modified conventional paper clip is further exasperated, since thicker documents need a clip with greater biasing force due to the tendency of inner sheets to slip due to an insufficient average biasing force between sheets.
In a different situation, an attempt to use the conventional spring steel type paper clips with documents having few sheets results in operational difficulties. For example, the all metal construction of this clip results in a heavy clip, which tends to bend the edge downwardly at the portion of the document to which it is applied making handling of the document during reading sometimes difficult. Further, the bulky construction of the clip tends to interfere with the fingers of the user reading the document and creates a problem in stacking a plurality of documents having this type of clip. More specifically, this type of clip has a greater dimensional thickness than the document due to its design preventing plural documents to be stacked flatly one on top of each other.
The paper clip of the present invention overcomes a number of problems mentioned above with the popular conventional paper clips. The two piece hingedly connected construction of the clip according to the present invention allows the clip to adequately handle a wide range of document thickness and number of individual sheets. Further, the clip according to the present invention utilizes a unique construction and spring, which results in greater biasing force for documents of increasing thickness. Thus, the varying spring biasing force correlates with the actual spring biasing force required to control and maintain the sheets properly biased together to prevent individual page slippage no matter what the document thickness.
Very importantly, the construction of the spring of the present invention lends itself to high speed and economic manufacturing and assembly. Since the clip can be made of plastic, the separate plate elements can be injection molded with accommodating hinge lugs and biasing spring. The cantilever type spring is molded extending from the inner surface of one or both plate elements. The free end of the cantilever spring engages and cooperates with an inner surface of the opposite plate element during operation. More specifically, the outer free end surface portion of the cantilever spring has a certain amount of curvature and engages with the inner surface of the opposite plate portion. This construction allows the cantilever spring to develop a greater biasing force due to the decreasing length of the moment arm from the base of the spring to the point of contact with the opposite plate portion.